The invention relate to an implement for working the surface of an agricultural field, especially to be used behind a tined harrow for the purpose of smoothing out the furrowed pattern left by the harrow tines, comprising a frame carrying a plurality of hubs each associated with a plurality of blades or knives to throw the surface earth laterally from the higher areas (the ridges) to the lower areas (the furrows), at least some of the knives being arranged relative pairs each of which is journalled in a intermediate bearing suspended from the frame by means of an arm. An implement of this type is known, e.g. from U.S. Pat. No. 4,382,474.
All of the knife assemblies may be arranged in this way so that each pair has its own suspended bearing-equipped hub, or several knife assemblies may have a common shaft or shaft section whereby the number of arms may be reduced relative to the number of knife assemblies. The knives incorporated in one or more pairs of assemblies may be firmly mounted on a common shaft or on connected shaft sections so that the knives in question rotate in unison but often it is preferred that the knife assemblies are freely and independently rotatable.
No matter which one of these arragements is used, plant remains such as straw material in stubble-fields as well as tough and long roots (couch-grass) may be very liable to restrain the rotation of the knife assemblies by penetrating into the hub area and wrapping up around the shafts, and to completely prevent the knife rotation when they are caught by the usual arms extending almost vertically from the knife assemblies to the carrying frame. Thus, when treating fields with a great amount of plant remains of the kind referred to, frequent interruptions of the work may be unavoidable, particularly when plant remains have to be torn off after having formed dense lumps or accumulations on the lower portions of the arms and thereby prevent rotation of the adjacent knife assemblies.